[Merged by Bors] - Use 3 bits of PipelineKey to store MSAA sample count #5826
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komadori
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Aug 29, 2022
| let msaa_bits = ((msaa_samples - 1) & Self::MSAA_MASK_BITS) << Self::MSAA_SHIFT_BITS; | ||
| MeshPipelineKey::from_bits(msaa_bits).unwrap() | ||
| let msaa_bits = | ||
| (msaa_samples.trailing_zeros() & Self::MSAA_MASK_BITS) << Self::MSAA_SHIFT_BITS; |
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Should this report an error in some way if the MSAA sample number is not a power of two?
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These checks are already inside the wgpu-rs.
Sample count must not only be the power of two, but also match the values chosen for the RenderTarget's attachments.
Weibye
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cart
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Aug 30, 2022
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bors r+ |
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Aug 30, 2022
Sample count always power of two. Thus, it is enough to store `log2(sample_count)`. This can be implemented using [u32::trailing_zeros](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.trailing_zeros). Then we can restore sample count with the `1 << stored`. You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware. Full table of possible variations: ``` original MSAA sample count stored loaded * 00000000000000000000000000000000 -> 000 -> 00000001 1 00000000000000000000000000000001 -> 000 -> 00000001 1 00000000000000000000000000000010 -> 001 -> 00000010 2 00000000000000000000000000000100 -> 010 -> 00000100 4 00000000000000000000000000001000 -> 011 -> 00001000 8 00000000000000000000000000010000 -> 100 -> 00010000 16 00000000000000000000000000100000 -> 101 -> 00100000 32 00000000000000000000000001000000 -> 110 -> 01000000 64 00000000000000000000000010000000 -> 111 -> 10000000 128 * 00000000000000000000000100000000 -> 000 -> 00000001 256 * 00000000000000000000001000000000 -> 001 -> 00000010 512 * 00000000000000000000010000000000 -> 010 -> 00000100 1024 * 00000000000000000000100000000000 -> 011 -> 00001000 2048 * 00000000000000000001000000000000 -> 100 -> 00010000 4096 * 00000000000000000010000000000000 -> 101 -> 00100000 8192 * 00000000000000000100000000000000 -> 110 -> 01000000 16384 * 00000000000000001000000000000000 -> 111 -> 10000000 32768 * 00000000000000010000000000000000 -> 000 -> 00000001 65536 * 00000000000000100000000000000000 -> 001 -> 00000010 131072 * 00000000000001000000000000000000 -> 010 -> 00000100 262144 * 00000000000010000000000000000000 -> 011 -> 00001000 524288 * 00000000000100000000000000000000 -> 100 -> 00010000 1048576 * 00000000001000000000000000000000 -> 101 -> 00100000 2097152 * 00000000010000000000000000000000 -> 110 -> 01000000 4194304 * 00000000100000000000000000000000 -> 111 -> 10000000 8388608 * 00000001000000000000000000000000 -> 000 -> 00000001 16777216 * 00000010000000000000000000000000 -> 001 -> 00000010 33554432 * 00000100000000000000000000000000 -> 010 -> 00000100 67108864 * 00001000000000000000000000000000 -> 011 -> 00001000 134217728 * 00010000000000000000000000000000 -> 100 -> 00010000 268435456 * 00100000000000000000000000000000 -> 101 -> 00100000 536870912 * 01000000000000000000000000000000 -> 110 -> 01000000 1073741824 * 10000000000000000000000000000000 -> 111 -> 10000000 2147483648 ```
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james7132
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Oct 28, 2022
Sample count always power of two. Thus, it is enough to store `log2(sample_count)`. This can be implemented using [u32::trailing_zeros](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.trailing_zeros). Then we can restore sample count with the `1 << stored`. You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware. Full table of possible variations: ``` original MSAA sample count stored loaded * 00000000000000000000000000000000 -> 000 -> 00000001 1 00000000000000000000000000000001 -> 000 -> 00000001 1 00000000000000000000000000000010 -> 001 -> 00000010 2 00000000000000000000000000000100 -> 010 -> 00000100 4 00000000000000000000000000001000 -> 011 -> 00001000 8 00000000000000000000000000010000 -> 100 -> 00010000 16 00000000000000000000000000100000 -> 101 -> 00100000 32 00000000000000000000000001000000 -> 110 -> 01000000 64 00000000000000000000000010000000 -> 111 -> 10000000 128 * 00000000000000000000000100000000 -> 000 -> 00000001 256 * 00000000000000000000001000000000 -> 001 -> 00000010 512 * 00000000000000000000010000000000 -> 010 -> 00000100 1024 * 00000000000000000000100000000000 -> 011 -> 00001000 2048 * 00000000000000000001000000000000 -> 100 -> 00010000 4096 * 00000000000000000010000000000000 -> 101 -> 00100000 8192 * 00000000000000000100000000000000 -> 110 -> 01000000 16384 * 00000000000000001000000000000000 -> 111 -> 10000000 32768 * 00000000000000010000000000000000 -> 000 -> 00000001 65536 * 00000000000000100000000000000000 -> 001 -> 00000010 131072 * 00000000000001000000000000000000 -> 010 -> 00000100 262144 * 00000000000010000000000000000000 -> 011 -> 00001000 524288 * 00000000000100000000000000000000 -> 100 -> 00010000 1048576 * 00000000001000000000000000000000 -> 101 -> 00100000 2097152 * 00000000010000000000000000000000 -> 110 -> 01000000 4194304 * 00000000100000000000000000000000 -> 111 -> 10000000 8388608 * 00000001000000000000000000000000 -> 000 -> 00000001 16777216 * 00000010000000000000000000000000 -> 001 -> 00000010 33554432 * 00000100000000000000000000000000 -> 010 -> 00000100 67108864 * 00001000000000000000000000000000 -> 011 -> 00001000 134217728 * 00010000000000000000000000000000 -> 100 -> 00010000 268435456 * 00100000000000000000000000000000 -> 101 -> 00100000 536870912 * 01000000000000000000000000000000 -> 110 -> 01000000 1073741824 * 10000000000000000000000000000000 -> 111 -> 10000000 2147483648 ```
ItsDoot
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Feb 1, 2023
Sample count always power of two. Thus, it is enough to store `log2(sample_count)`. This can be implemented using [u32::trailing_zeros](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.trailing_zeros). Then we can restore sample count with the `1 << stored`. You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware. Full table of possible variations: ``` original MSAA sample count stored loaded * 00000000000000000000000000000000 -> 000 -> 00000001 1 00000000000000000000000000000001 -> 000 -> 00000001 1 00000000000000000000000000000010 -> 001 -> 00000010 2 00000000000000000000000000000100 -> 010 -> 00000100 4 00000000000000000000000000001000 -> 011 -> 00001000 8 00000000000000000000000000010000 -> 100 -> 00010000 16 00000000000000000000000000100000 -> 101 -> 00100000 32 00000000000000000000000001000000 -> 110 -> 01000000 64 00000000000000000000000010000000 -> 111 -> 10000000 128 * 00000000000000000000000100000000 -> 000 -> 00000001 256 * 00000000000000000000001000000000 -> 001 -> 00000010 512 * 00000000000000000000010000000000 -> 010 -> 00000100 1024 * 00000000000000000000100000000000 -> 011 -> 00001000 2048 * 00000000000000000001000000000000 -> 100 -> 00010000 4096 * 00000000000000000010000000000000 -> 101 -> 00100000 8192 * 00000000000000000100000000000000 -> 110 -> 01000000 16384 * 00000000000000001000000000000000 -> 111 -> 10000000 32768 * 00000000000000010000000000000000 -> 000 -> 00000001 65536 * 00000000000000100000000000000000 -> 001 -> 00000010 131072 * 00000000000001000000000000000000 -> 010 -> 00000100 262144 * 00000000000010000000000000000000 -> 011 -> 00001000 524288 * 00000000000100000000000000000000 -> 100 -> 00010000 1048576 * 00000000001000000000000000000000 -> 101 -> 00100000 2097152 * 00000000010000000000000000000000 -> 110 -> 01000000 4194304 * 00000000100000000000000000000000 -> 111 -> 10000000 8388608 * 00000001000000000000000000000000 -> 000 -> 00000001 16777216 * 00000010000000000000000000000000 -> 001 -> 00000010 33554432 * 00000100000000000000000000000000 -> 010 -> 00000100 67108864 * 00001000000000000000000000000000 -> 011 -> 00001000 134217728 * 00010000000000000000000000000000 -> 100 -> 00010000 268435456 * 00100000000000000000000000000000 -> 101 -> 00100000 536870912 * 01000000000000000000000000000000 -> 110 -> 01000000 1073741824 * 10000000000000000000000000000000 -> 111 -> 10000000 2147483648 ```
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Sample count always power of two. Thus, it is enough to store
log2(sample_count).This can be implemented using u32::trailing_zeros. Then we can restore sample count with the
1 << stored.You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware.
Full table of possible variations: